There are many areas of electronics where it is desired to propagate signals, either analog or digital signals, from one voltage domain to another voltage domain. Examples of such systems include power monitoring or motor control where the voltages in a first voltage domain can range up to 1200 volts or more referenced to a first reference voltage, whereas the control electronics may need to interface with other systems, and is typically in a voltage domain of only a view volts, for example 5 volts, referenced to a second reference voltage, typically ground. Such an arrangement is shown in FIG. 1 where the voltages in the first voltage domain (VDOM1) extend between voltage V1 and voltage VREF1, and where the voltages in the second voltage domain (VDOM2) extend between voltage V2 and VREF2. Transmission of signals between these first and second voltage domains is typically done by way of an isolator 10. The isolator 10 may provide galvanic isolation between the two voltage domains. Isolators may include opto-electric couplers, but other technologies are possible, for example capacitors 12, as shown in FIG. 2, or transformers 14, as shown in FIG. 3. Typically, capacitive and transformer based isolation may be preferable and can be provided in chip scale packages (e.g., an integrated circuit form). For example, the capacitive and transformer isolation may be provided in monolithic integration or as two or more dies within a chip scale package (integrated circuit package).
Such isolators can be exposed to the full voltage difference between the first and second voltage domains VDOM1 and VDOM2. In some circumstances, these voltage domains might be subject to transient over voltages, such that either the isolator has to be significantly over specified in terms of its maximum voltage, possibly with an impairment in its ability to transmit data, or otherwise there may be a risk of the device becoming damaged. Furthermore, in the case of transformer based isolators, it may also be desirable to avoid the voltage, acting within a coil, from becoming too great, which may create additional electrical stresses leading to failure of the transmission path within the isolator even if the isolation between the two voltage domains does not fail. For example, in transformers formed in integrated circuits excess voltage at a node of the transformer might cause excess current flow that could damage the transformer.